Wear prognosis method and maintenance method

ABSTRACT

A wear prognosis method and a maintenance method for an earth working machine are disclosed, along with an apparatus for performing the method. Provision is made that the current wear state of one or more earth working tools is sensed. The residual wear capacity until the wear limit is reached is then ascertained from the current wear state.

BACKGROUND OF THE INVENTION

In the context of road reconstruction by milling, and the removal ofmineral deposits with a surface miner (also by milling), the earthworking tools that are used, and in particular the milling bits, aresubject to a continuous wear process. Replacement is advisable once thetools reach a specific wear state, since otherwise the ongoing processloses efficiency. A distinction must be made here among a variety ofwear states that result in replacement of a milling bit or bit holder:

-   1. Bit replacement because sufficient wear material (in particular    carbide metal at the tip) is no longer present. The penetration    resistance becomes too high and the efficiency thus decreases (too    much frictional loss); the wear is predominantly rotationally    symmetrical.-   2. Bit holder replacement because the wear limit has been reached    (wear occurs on the holder at the contact surface between bit and    holder). This wear is usually symmetrical.-   3. Rotationally asymmetrical wear on the bit tip and/or bit head due    to insufficient rotational movement of the bit during the milling    process. The consequences are a poor milling pattern as well as the    risk of tool breakage, since the bracing effect of the bit head is    lost.-   4. The bit holder can furthermore be subject to additional    rotationally asymmetrical wear.-   5. Bit breakage.

In addition, worn and/or broken bits can result in secondary damage tothe bit holders, and worn bit holders can cause secondary damage to themilling drum. Timely replacement of the bit and/or bit holder istherefore necessary and reduces costs. If the bits and/or bit holdersare changed too soon, however, this procedure is likewise not optimum interms of cost, since the bits and bit holders are consumable parts andtherefore very cost-intensive. Wear potential that is still available isthen not being correctly utilized. The wear state of bits and bitholders has hitherto been assessed by visual inspection by the machinedriver. For this purpose the machine operator must shut off the machine(switch off engine and decouple drum from the drive train). He must thenopen the rear drum hatch so the milling drum can be visually inspected.

The milling drum is then rotated by means of a second drive system sothat the entire milling drum can be inspected. The drum inspection taskcan also be handled by a second operator. The wear state of the bitholders is usually assessed by way of so-called “wear markings.” Thewear state of the bits can be determined by way of the longitudinal wearand the rotational symmetry of the wear pattern.

Monitoring the wear state of bits and holders is very time-intensive,and is unproductive since nothing can be produced during that time. Theoverall process is disrupted and availability is thus additionallydecreased. In addition, because of the highly subjective nature of theassessment, the risk exists that the wear potential of holders and bitswill not be optimally utilized.

DE 102 03 732 A1 (U.S. Pat. No. 7,422,391) discloses an apparatus inwhich operation can be optimized by monitoring operating states ofmachine components that participate directly or indirectly in themilling process. Among other factors, the wear state of the bits is alsoassessed by evaluating a variety of machine parameters and variables.The problem that exists during operation of the milling machine is thatthe milling process and the substrate itself, whose properties fluctuateconsiderably, have a large influence on evaluation of the operatingstate of components.

AT 382 683 B discloses a mining machine in which the cutting drum ismonitored in noncontact fashion, using photoelectric barriers thatdetect the presence of the bits. A quantitative wear evaluation is notpossible with this method.

DE 10 2008 045 470 A1 (U.S. Pat. No. 8,386,196) discloses a method forquantitative wear identification. Here the position in space of at leastpoint on the earth working tool is sensed. This measurement result isthen compared with a reference value so that the wear on the tool can besensed quantitatively.

As already mentioned above, the material properties of the substratebeing processed change during the working process. In mining, forexample, it can happen that while traveling over a deposit of materialto be removed, the hardness of the raw material suddenly rises (“hardspot”). Increased wear then occurs on the tools.

In order to avoid damage to the cutting equipment due to unpredictableworking conditions, for safety reasons the tools are on occasionswitched out too soon.

SUMMARY OF THE INVENTION

An object of the invention is to furnish a method that makes possible aneconomically optimized working process.

This object of the invention is achieved with a method for wearprognosis for an earth working machine, in particular a road millingmachine, a surface miner, or the like, the current wear state of atleast one earth working tool, in particular of a bit and/or a bitholder, being sensed. This can be effected, for example, using themethod according to DE 10 2008 045 470 A1 (U.S. Pat. No. 8,386,196)described above. From the interim result thereby obtained, according tothe invention the residual wear capacity until a predefined wear limitis reached is then ascertained in a further method step. A wear state atwhich the earth working tool must be replaced is consequently defined.By incorporating local conditions, for example, it is then possible, forexample, to ascertain the specific remaining service life of the earthworking tool. This yields an optimized working process. In particular,the machine operator can now be given specific information that provideshim with data regarding the residual wear capacity of the earth workingtool. The result is to prevent timely changing of the earth working toolfrom being neglected, or to avoid premature changing of the earthworking tool with the economic disadvantages associated therewith.

According to a preferred variant of the invention, provision can be madethat the remaining working output of the earth working machine until thewear limit of the earth working tool is reached is ascertained from theresidual wear capacity based on at least one characteristic value or onthe derivation of at least one characteristic value. What is ascertainedas the remaining working output can be, for example, the milling output,in particular the mass of material that can still be milled and/or thevolume of material that can still be milled and/or the remaining traveldistance for the earth working machine or the remaining working time forthe earth working machine. These parameters give the machine operatorinformation that can be unequivocally implemented.

An effective wear prognosis can be generated by comparing the currentwear state of the earth working tool with a reference value reproducingat least a portion of the earth working tool in the worn state, in orderto ascertain the residual wear capacity. The reference value can be, forexample, a reference contour (partial contour or complete contour), oneor more reference points, a reference volume (partial volume or totalvolume), or the location or direction of the longitudinal center axis ofthe earth working tool.

The reliability of the working process is additionally improved whenprovision is further made that the wear state of several or of all earthworking tools of the earth working machine is ascertained; and that theearth working tool exhibiting the least residual wear capacity is takeninto account for ascertaining the remaining working output until thewear limit is reached. For example, a few representative earth workingtools can be selected so that a detailed wear statement can be made. Ifall the earth working tools are monitored, an almost one-hundred-percentwear statement becomes possible.

A method according to the present invention for wear prognosis can becharacterized in that a working area within which two or more earthworking machines are being used is defined; and that the current wearstate of at least one earth working tool of an earth working machine isascertained, and that the at least one characteristic value or thederivation of the one or more characteristic values is derived from thepreviously produced milling output of said at least one earth workingtool and from the wear, corresponding thereto, of the at least one earthworking tool. A reference working process is therefore carried out. Forexample, firstly unworn tools or tools that already exhibit partial wearare used. The working process is then carried out using a workingmachine of this kind. During this process, various parameters can thenbe acquired, in particular the milling output produced. The millingoutput produced can be, for example, as already described above, themass of material milled, the distance traveled, etc. A correlation canthen be arrived at by differential analysis between the previously knownwear state and the wear state existing after the working process. Thisindicates the wear that has occurred on the tools in the context of theworking output produced. From this, one or more characteristic valuescan then be derived. These characteristic values can then be used inorder to ascertain, for any given wear state (and residual wear capacityresulting therefrom), the working output still to be produced (forexample, until the wear limit is reached).

These characteristic values can correspondingly be ascertained andutilized directly on the working machine that is present, or they can beconveyed to at least one further earth working machine that, inparticular, is working a comparable substrate.

In another embodiment of the invention, the at least one characteristicvalue is ascertained in consideration of the material properties, inparticular the abrasiveness and/or material hardness, of the substrateto be worked.

For practical reasons, the at least one characteristic value can beascertained preferably in consideration of a material hardness rangethat contains the material hardness of the substrate being worked.Additionally or alternatively, provision can also be made that thecharacteristic value is ascertained in consideration of an abrasivenessrange that contains the abrasiveness of the substrate to be worked. Forexample, selective measurements from the sector to be worked can berepresentatively performed, and the values for material hardness and/orabrasiveness can be determined in that context.

In mining it is usual to take samples from an area that is to be worked,in particular to perform sample boring operations. The samples are theninvestigated and the raw material's parameters are identified. Accordingto an inventive alternative, these results can also be used directly inthe method according to the present invention, so that thecharacteristic values/material properties for inferring thecharacteristic values can be ascertained therefrom.

It is also conceivable for the machine operator to be able to select,from a list of different substrate categories, the category suitable forthe substrate currently to be worked, and for the material propertiesfor ascertaining the at least one characteristic value to be associatedwith said substrate categories. The result is that the machine operatorcan simply assess the substrate on site in consideration of hisaccumulated experience, and can make a corresponding selection. Forexample, one or more characteristic values are associated with thissubstrate category in a database. When the substrate category isselected, these characteristic values are then read out from thedatabase and processed via software in order to ascertain the residualwear capacity and thus the remaining working output. This method has theadvantage that the machine operator can respectively determine theresidual wear capacity and the remaining working output directly onsite, and can also implement an adaptation in particular as substratecategories change.

Alternatively or additionally, it is also conceivable to indirectlysense the material properties of the substrate to be worked. Provisioncan be made here that the material properties for ascertaining the atleast one characteristic value are ascertained during working operationon the basis of machine parameters. For example, the milling depth,machine advance, milling drum rotation speed, torque applied to theprocessing tools, and/or power output currently being delivered by thedrive engine can be ascertained. These machine parameters provideinformation regarding the material properties, in particular theabrasiveness or hardness, of the substrate to be processed. The rotationspeed, torque, and delivered power output can be taken directly from theengine control unit (ECU) of the drive engine. The first two parameterscan be furnished by the machine control system.

A particularly preferred inventive variant is such that firstly thecurrent wear state and the residual wear capacity are ascertained; andthen the working output produced by the earth working machine, inparticular the milling output and/or the machine data occurring duringthat working process, are monitored. The actual wear state of the earthworking tool can then be ascertained, for example calculated,continuously during the working process. If, for example, a change inthe substrate category then occurs or if a new processing task isundertaken, this most recently ascertained actual wear state can beemployed as a current wear state for purposes of the invention, and theresidual wear capacity available for the task at hand can then beascertained.

A calculation unit, with which a memory unit is associated, ispreferably provided. The one or several characteristic values, or thederivation of the characteristic values, is/are stored in the memoryunit. The current wear state can be sensed with a sensing device. Theremaining working output until the wear limit of the earth working toolsis reached can be ascertained by means of the calculation unit using thecurrent wear state, the residual wear capacity resulting therefrom, andthe characteristic value or values or the derivation thereof. Theresidual wear capacity can be ascertained in the calculation unit on thebasis of the wear state and the reference contour. The calculation unitand/or the memory unit can be, for example, directly associated with theearth working machine. It is also conceivable, however, for thecalculation unit and/or the memory unit to be associated with a separatesystem unit. When provision is made for separate association, the earthworking machine can then be in mutual communication with the system unitvia a preferably wireless remote data transfer link. Depending on thewhereabouts of the earth working machine, the latter can then besupplied with relevant parameters; in particular, the residual wearcapacity and/or remaining working output can be conveyed. Among theadvantages of this is the fact that when multiple earth working machinesare being used in one working area, they can each individually retrievethe necessary data from the system unit.

The characteristic values can be stored in the calculation/memory unitas a function of location. For example, a map of, for example, a minecan be stored, in which map different characteristics values areassociated with different locations. The machines can possess GPS, orthe operator inputs his location, and the corresponding characteristicvalues are used. It would also be possible, especially in the context ofan external calculation unit, for only the material properties to bestored and for the characteristic values to be ascertained by themachine itself on the basis of those material properties.

The object of the invention is also achieved by a maintenance method foran earth working machine, in which a plurality of earth working tools,in particular bits and/or bit holders, are used. In this context, thecurrent wear state of at least one earth working tool is sensed.Proceeding from that wear state, the residual wear capacity of the earthworking tool is then ascertained. Before the wear limit of the earthworking tool is reached, a technician is then informed so thatmaintenance can be carried out. In the context of this maintenancemethod, a prognosis regarding the remaining milling output can becreated in consideration of the residual wear capacity that isascertained. A maintenance unit can be informed in timely fashion beforesaid milling output has been entirely produced. This can occur, forexample, in automated fashion by means of a signaling device of theearth working machine. This signaling device outputs a correspondingsignal that can be conveyed preferably wirelessly to a maintenancestation. The working output of the earth working machine remaining untilthe wear limit of the earth working tool is reached can be signaled inthe form of the distance that can still be milled, the volume or massthat can still be milled, and/or the remaining service life. In thecontext of an earth working machine, for example, it is possible for theresidual wear capacity of the earth working tool to be ascertainedbefore a planned working process is undertaken. The maintenanceintervals for that working process can then already be predicted oroptimized in advance as a function of the predicted wear for the millingtask.

Whereas the material characteristic values and residual wear capacitycan be taken into account in order to ascertain the remaining workingoutput, here conversely the expected bit change is ascertained using thematerial properties and the remaining working output.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in further detail below with referenceto an exemplifying embodiment depicted in the drawings, in which:

FIG. 1 is a side view of a bit, namely a round shank bit for a roadmilling machine, a mining machine, a surface miner, or the like, whichis inserted into the holder of a quick-change holder tool for suchmachines;

FIG. 2 is a diagram showing the bit head of the bit according to FIG. 1;

FIGS. 3 to 7 are diagrams showing various wear states of the bit head;

FIG. 8 is a schematic depiction and side view of a milling machine;

FIG. 9 shows a milling drum of the milling machine in accordance withFIG. 8, having an example of a surveying device based on thetriangulation principle;

FIG. 10 shows the milling drum in accordance with FIG. 8, having analternative embodiment of the surveying device based on a shadow-castingmethod; and

FIG. 11 schematically depicts a working situation with two millingmachines.

DETAILED DESCRIPTION

FIG. 1 shows, as an example of an earth working tool, a bit 10 as knownfrom the existing art and described by way of example in DE 38 18 213A1. Bit 10 comprises a bit head 12 and a bit shank 15 shaped integrallythereonto. Bit head 12 carries a bit tip 11 made of a hard material, forexample of carbide metal.

This bit tip 11 is usually soldered onto bit head 12 along a contactsurface. A circumferential pull-out groove 13 is recessed into bit head12. This groove serves as a tool receptacle, such that a removal toolcan be set in place and bit 10 can be removed from a bit holder 70.

Bit shank 15 carries a longitudinally slotted cylindrical clampingsleeve 21. This is held on bit shank 15 in lossproof fashion in thedirection of the longitudinal dimension of bit 10, but freely rotatablyin the circumferential direction. A wear protection washer 20 isarranged in the region between clamping sleeve 21 and bit head 12. Inthe installed state, wear protection washer 20 is braced against acountersurface of a bit holder 70 and against bit holder 70, facing awayfrom the underside of bit head 12.

Bit holder 70 is equipped with a projection 71 into which a bitreceptacle 72 in the form of a cylindrical bore is recessed. In this bitreceptacle 72, clamping sleeve 21 is held with its external peripheryclamped against the inner wall of the bore. Bit receptacle 72 opens intoa drift opening 73. Through this, a drift punch (not shown) can beintroduced for the purpose of removing bit 10. Said punch acts on theend of bit shank 15 in such a way that bit 10 is pushed out of bitreceptacle 72 as the clamping force of clamping sleeve 21 is overcome.

As is evident from FIG. 1, extension 71 is equipped in a cylindricalregion below wear protection washer 20 with two circumferential grooves.These grooves serve as wear markings 74. During operational use, wearprotection washer 20 rotates and, in that context, can create wear (bitholder wear) on the support surface of projection 71. When the supportsurface has been worn away to the extent that the second wear markinghas been reached, bit holder 70 is considered to be worn in such a waythat it must be replaced.

Bit holder 70 comprises an insertion projection 75 that is introducibleinto an insertion receptacle 82 of a base part 80 and can be clampedthere by means of a clamping screw 83.

Clamping screw 83 presses an abutment surface 76 of bit holder 70 onto asupport surface 84 of base part 80. Although this is not depicted infurther detail in FIG. 1, base part 80 itself is welded via itsunderside 81 onto the milling drum tube of a milling drum.

Noncontact surveying of bit head 12 is performed in order to ascertainthe current wear state of bit 10 installed on the bit holder, a definedpoint or multiple points of bit head 12 being measured/ascertained as aposition value. FIG. 2 is a side view of the contour of an unworn bithead 12. This contour is illustrated in a diagram, the dimension of bithead 12 in the direction of the longitudinal bit axis of bit 10 (X axis)being plotted against the dimension in the width direction(perpendicular to the longitudinal center axis, i.e. Y axis). Thecontour of bit head 12 (including bit tip 11) is assembled from aplurality of measured points, and the linear boundary (contour line)represents an interpolation of these position values.

Surveying of a milling drum 35 (see FIGS. 9 and 10) can be performedwhen bit 10 is in the unworn, worn-out, or partly worn state. Thesepoints, the calculated bit head contour, or even only a singlemeasurement point can then be acquired and stored as a reference valuein a memory unit.

FIG. 3 shows a variety of measured images of a bit 10, bit head 12 beingdepicted in the unworn state and in three measured wear states V1 to V3.Wear state V3 represents the state in which bit 10 is no longer suitablefor further processing and must be replaced. The wear can be ascertainedby comparing the reference value (contour in the unworn state) with therespectively measured current bit head contour (wear states V1, V2, orV3) that reproduce the position value.

The contours must be aligned with one another. Because of holder wear orother error sources, unworn contour regions are not necessarily locatedat the same absolute positions (or relative positions with respect tothe drum rotation axis). In order to correlate the contours there is afurther need for reference features that are uniquely identifiable,occur in the unworn and worn state, and thus permit alignment andconclusive evaluation. Pull-out groove 13, wear markings 74, wearprotection washer 20, or other salient regions that are subject tolittle or no wear can serve as reference features.

As illustrated by FIG. 3, the length of bit head 12 decreases duringoperational use. By differentiating the contour lines in a circuit unitit is possible to generate a statement regarding the wear state, whichcan be made visible to the user, for example, in a display unit. Insteadof surveying the entire contour of bit head 12, it is also possible tosense only a portion of the contour or a single point, in particular thefront end of bit tip 11, as a position value. Further detail in the wearstatement can be achieved if the wear on bit tip 11 and on bit head 12(without bit tip 11) is sensed separately.

This can easily be done using the position (attachment pointTP/attachment line 18), known a priori, at which bit tip 11 attaches tobit head 12 in the unworn state.

When the measured wear states V1 to V3 are overlaid on the unworncontour of bit head 12, as shown in FIG. 2, it is then possible toascertain the total wear volume by integrating the measured contoursalong the X axis. In FIG. 4 the wear volume is shown as hatched areas.

The wear volume that constitutes a position value can thus be comparedwith a reference value. The reference value can be constituted by afunctional relationship or a characteristics diagram, different wearvolumes being correlated with associated wear states (for example, A mm³of wear volume corresponds to B% wear). From the position, known apriori, of attachment point TP/attachment line 18, the tip wear 16 andhead wear 17 can then also be separately ascertained by differentiation.This wear detection process provides the user, for example, with aqualitative statement as to whether bit 10 is still suitable forspecific milling tasks. For example, a bit that has not yet reached itswear limit but exhibits some tip wear can no longer be used, forexample, for precision milling work.

In the method according to FIGS. 3 and 4, the measured position valuesare overlaid on the reference values. During the working process, notonly bit head 12 but also the bit holder becomes worn. The latter wearsaway in the direction of the longitudinal center axis of bit 10.Isolated identification of the longitudinal wear on the bit holder inthis direction can now easily be achieved by the fact that the magnitudeof the displacement of the position value toward the reference value inorder obtain the overlays indicated in FIGS. 3 and 4 (shifting bit head12 in the direction of the X axis, for example until the pull-outgrooves of the individual wear states are superimposed) yields anabsolute value for the wear on the bit holder. The total displacement ofbit tip 11, minus said wear value, then separately indicates the bitwear.

FIG. 5 shows a variant method in which a wear statement is arrived atbased on surveying one uniquely identifiable feature on the bit. Thefeature, or the surroundings of said feature, should be subject tolittle or no wear. According to FIG. 5, pull-out groove 13, a portion ofpull-out groove 13, or a point (for example the groove base) on pull-outgroove 13 is used as a unique feature and reference criterion.

The distance from this feature to the position of the free end of bittip 11 (position value) is then further ascertained. It is then easy toascertain the longitudinal wear in this manner. If the position of bittip 11 is known, then once again, as described above, the bit holderwear can also be identified. Alternatively or additionally, as definedin FIG. 4, the wear volume and the associated wear lengths—X₁ (currentlymeasured length of partly worn bit), X₂ (worn-out length), and Xges(total length of unworn bit)—can also be ascertained.

Relative measurement using a uniquely identifiable feature as referencepoint has the advantage that wear detection can be performed even when areference measurement is not available, for example because the lengthof the replaced bit 10, or the wear state of bit 10 or of the bitholder, is not known.

FIG. 3 shows the change in the bit head contour as wear proceeds. Thedecreasing length of bit head 12 is evident. If the measured bit headcontours are respectively shifted to the point of the maximum length ofbit 10 (FIG. 6), the increasing wear state of bit 10 is evident on theone hand from the change in head angle (the angle becomes flatter as bitwear increases) and on the other hand from the increasing volume of bithead 12 when the area under the contour curve is integrated from therespective tip over a specific length. A functional relationship canthus be created between the head volume/area and the absolute bit lengthfor a specific bit type, for example by means of experiments carried outa priori in order to ascertain the reference values.

Once this relationship is known, the length of bit 10 can be ascertainedby measurement/integration of the respectively current head volume. Thismethod requires, however, that bit tip 11 have a cross section thatincreases in the longitudinal direction of the bit. The integration pathis preferably defined so that integration does not occur into the headregion even for completely worn-out bits 10, since head erosion distortsthe result.

This method has the advantage of not requiring a reference point that issubject to little wear. Such a reference point sometimes is not presentor is very difficult to identify.

The average between the upper and lower contour line can, for example,be calculated in order to identify the degree of wear asymmetry. FIG. 7shows the contour lines, and their averages, for a new bit tip 11 andfor one that is worn rotationally symmetrically (R1) and rotationallyasymmetrically (R2). It is evident that with the asymmetrically worn bit10, the center line M2 of the two contour lines exhibits a certain slopewith respect to the longitudinal bit axis. The angular position couldeasily be evaluated in order to determine the degree of wear asymmetry.The location/deviations of several contour lines could, however, also beidentified/ascertained directly.

Asymmetrical wear on bit head 12 can be identified using the samemethod. Usually, however, an asymmetrically worn bit tip 11 will beaccompanied by an asymmetrically worn bit head 12. An analysis of bittip 11 is thus sufficient.

FIG. 8 symbolically depicts a milling machine 30, for example a surfaceminer, a road milling machine, or the like, in which a machine body 32is carried by four columnar drive units 31. Road milling machine 30 canbe operated from a control station 33. A milling drum 35 is arranged ina milling drum box 34.

In order to measure the wear state according to one of the methodsdescribed above, a light source 50 and a camera 40 are associated withmilling drum 35. Milling drum 35 is shown more clearly in FIG. 9. Aplurality of bit holder quick-change systems, each having a bit holder70, are mounted on the surface of a milling tube 35.1 of milling drum35. A bit 10 is held in each bit holder 70. In the present example, bitholders 70 are welded directly onto milling drum 35.

It is also conceivable, however, to use the quick-change bit holdersystem according to FIG. 1, in which case base part 80 is then weldedonto milling drum 35.

An optical system, in which an elevation line of the drum surface isrespectively surveyed in a kind of “scanning” operation, is used as anapparatus for surveying the bit contours. The measurement principle thatcan be used here is, for example, a triangulation method in which thedrum surface is illuminated, for example, by a light source 50, forexample a laser line. When the laser line thereby generated is observedby a camera 40 at a different angle, elevation differences on the drumsurface (caused, for example, by bits 10) are evident as shifts of theseprojection lines. If the angular difference between camera 40 and lightsource 50 is known, the elevation coordinates can be calculated. Byrotating milling drum 35 it is thus possible to create an elevationprofile of the drum's enveloping surface, from which profile the contourline of the individual bits 10 can then be read out. A further opticalmeasurement principle for surveying the elevation and/or geometry ofbits 10 is the shadow-casting method according to FIG. 10. This methodmakes use of the fact that bits 10 moving through a light curtaingenerated by a light source 50 generate a shadow contour that can beobserved and evaluated by a camera 40. The great advantage of thismethod lies in the fact that it is possible to work with a single camerarow, in principle like a document scanner. This means that, inparticular, even milling drums 35 having a large diameter and highrotation speeds can be surveyed with sufficient resolution.

The method described with reference to FIG. 10 can be modified inaccordance with an alternative variant embodiment of the invention. Hereonce again a light curtain in the form of a light plane is generatedusing a light source 50. This light plane extends parallel to thelongitudinal center axis of milling drum 35 and tangentially to the drumsurface. The light plane is configured so that in the case of a rotatingmilling drum 35, the tips of bits 10 are the first to penetrate throughthe light plane.

They then cast a shadow that can be sensed by camera 40. Bits 10 areguided through the light plane over a specific drum rotation angle untilthey then sink again below the light plane.

A reference measurement can be performed with unworn bits 10/bit holders70. Here the time at which bit 10 passes through the light plane (entryor exit) is sensed, and the associated rotation angle of milling drum 35is sensed. After operational use, a corresponding measurement is thenperformed on the partially worn (worn out) bit 10. Because of thereduced length as compared with an unworn system, bit 10 passes throughthe light plane at a later time, and sinks below it sooner. Thecorresponding rotation angle of milling drum 35 can then be ascertainedas a position value. These rotation angles are then compared with therotation angles for the unworn system (reference value). A calculationof the wear state can then be made from the angle difference bydifferentiation, or the rotation angle difference is employed directlyas a wear criterion.

During the milling process, for example in phases during whichmeasurement does not occur, the measurement system is usefully stowed ina corresponding protective apparatus. If a second camera 40 is used, forexample, direct surveying of the elevation geometry can be performedwithout an additional illumination source.

Alternatively, by correspondingly placing a second camera, additionalmeasurements of the contours can be carried out so that the overallinformation density is increased and the detection probability forasymmetrical wear states is raised.

Alternatively, the position of bit tip 11 or the location of the bithead contour can also be sensed in at least one step using other sensorequipment that measures distance (e.g. ultrasonic sensors, proximityswitches).

As already explained in detail above, the following can be ascertainedusing the measurement methods described above:

-   1. The current wear state V₁, V₂, V₃ of an earth working tool (bit    10),-   2. The wear resulting from comparison of a reference value (bit 10    in the unworn or partially worn state) with the current wear state    V₁, V₂, V₃.

In order for the wear according to item 2. above to occur, the earthworking machine must have produced a certain milling output. Thismilling output can be measured, for example as a number of tons milled(milled mass), as a milled volume, and/or as a milled distance, etc. Themilling output can in particular be ascertained directly on an earthworking machine. If the earth working machine is equipped with ameasurement system described above, the wear (see 2.) can also be senseddirectly and the characteristic value or values can be derived inconjunction with the ascertained milling output.

Based on the measured current wear state V1, V2, and with a knowledge ofthe wear limit V3 of bit 10, the residual wear capacity of bit 10 cannow be ascertained. For example, if the measured free end of bit tip 11according to FIG. 5 represents the current wear state constituting aposition value, the distance to the reference contour R reproducing thewear state, and thus the residual wear length (Xges—X1), can thus beascertained as the residual wear capacity by differentiating in the Xaxis direction. Additionally or alternatively, the residual wearcapacity can be ascertained as the residual wear volume of bit tip 11remaining until the wear limit V3 is reached. This is done, for example(see discussion above of FIG. 4), by overlaying the measured wear stateV1, V2 of the bit contour on the reference contour R in the worn stateV3. The residual wear volume can then be ascertained by integrationalong the X axis.

The change in wear state is influenced by material properties, forexample by the hardness and/or abrasiveness of the milled material. Thematerial properties can be sensed indirectly. For example, samples canbe taken (e.g. sample boring operations) in the area to be milled, andcan be evaluated.

It is also conceivable to use existing mining category systems. Generalhardness and abrasiveness categories are defined for mines (e.g. “hard,non-abrasive,” “moderate, non-abrasive,” “soft, abrasive,” etc.). Fromthese categories, the category matching the planned route of travel canbe selected.

The material properties can also be ascertained by evaluating machinedata (e.g. rotation speed of the milling drum, torque, advance, andmilling depth), since the material properties correlate directly withthese machine data.

Characteristic values can be ascertained as a function of the millingoutput and/or the material properties. These characteristic valuesindicate the change in the wear state which is to be expected for aspecific milling output and/or for predefined material properties.

Based on the residual wear capacity and in consideration of one or morecharacteristic values, the remaining working output can then be signaledto the machine operator. He can be informed, for example, as to themilling output that can still be produced (e.g. mass or volume ofmaterial that can still be milled, number of truckloads that can stillbe milled, travel distance that can be milled, or milling time).

If the milling output per unit time for an earth working machine isknown, it is also possible in particular to indicate the time remaininguntil the next tool change. The milling output per unit time can becontinuously ascertained on the basis of current machine parameters(advance, milling depth). It can also be previously known based onmilling work already carried out at the same location.

FIG. 11 illustrates a milling area F, for example a mine, in whichmultiple milling machines 30 are working. Milling area F contains a rawmaterial deposit, and the material properties change in sub-areas F₁,F₂, F₃.

These sub-areas F₁, F₂, F₃ are associated in mine maps with hardness andabrasion categories (see above). Before work begins, the measurementsystem (for example, camera 40) ascertains the current wear state V₁, V₂and conveys this, as well as the current position of the machine, via atransmission and reception apparatus 61 to an external system unit 60.There, in consideration of the calculated residual wear capacity and ofone or more characteristic values, the remaining milling output untilthe wear limit V3 is reached is ascertained. The characteristic valueideally takes into account the planned route of travel and the varioushardness and abrasion categories, associated therewith, in sub-areas F₁,F₂, F₃, as well as the expected wear related to the hardness andabrasion categories. The ascertained working output until the wear limitV3 is reached is signaled back to milling machine 30.

Milling machine 30 depicted on the right in FIG. 11 has already traveledover sub-areas F₁ and F₂ and has acquired measured values in thatcontext. These measured values can be evaluated. For example, it ispossible to sense what kind of wear occurs with what milling output.This result, or the characteristic values resulting therefrom, can thenbe respectively made available to the second milling machine in FIG. 11in order to improve the quality of the wear prognosis.

The invention claimed is:
 1. A method of determining wear for an earthworking machine having at least one earth working tool, the methodcomprising: prior to an earth working operation of the earth workingmachine: sensing one or more position values corresponding to a currenttool contour of the at least one earth working tool; determining a firstwear state by comparing the one or more position values of the currenttool contour with a reference tool contour aligned therewith; and duringthe earth working operation of the earth working machine: continuouslydetermining an actual work output of the earth working machine from oneor more machine parameters; determining a second wear state of the atleast one earth working tool, based on a calculated change in wear fromthe first wear state corresponding to the continuously determined actualwork output and a material property of a corresponding substrate workedsince beginning the earth working operation; predicting a remaining workoutput until a third wear state of the at least one earth working tool,based on an expected change in wear from the second wear statecorresponding to a material property of a substrate yet to be workedduring the earth working operation.
 2. The method of claim 1, whereinthe at least one earth working tool includes a bit and/or a bit holder.3. The method of claim 1, wherein the remaining work output for theearth working machine is determined in terms of at least one of: amilling output of the earth working machine; a mass of material to bemilled by the earth working machine; a volume of material to be milledby the earth working machine; a remaining travel distance for the earthworking machine; and a remaining working time for the earth workingmachine.
 4. The method of claim 1, during the earth working operationfurther comprising: continuously determining the material property ofthe substrate being worked by the earth working machine, and reading outat least one characteristic value from a database, said characteristicvalue derived from the determined material property and corresponding toa change in the wear state which is expected for a given work output inthe substrate to be worked.
 5. The method of claim 4, furthercomprising: identifying a working area within which two or more earthworking machines are being used, wherein a characteristic value for thefirst one of the earth working machines is derived from a previouslyproduced work output of the first one of the earth working machines anda change in wear state of the at least one earth working tool of thefirst one of the earth working machines corresponding to the previouslyproduced work output; and wherein the characteristic value for the firstone of the earth working machines in the working area is used todetermine a remaining work output for a second one of the earth workingmachines in the working area.
 6. The method of claim 4, wherein the atleast one characteristic value corresponds to a material hardness rangeincluding a material hardness of a substrate to be worked by the earthworking machine.
 7. The method of claim 4, wherein the at least onecharacteristic value corresponds to an abrasiveness range including anabrasiveness of a substrate to be worked by the earth working machine.8. The method of claim 4, further comprising determining the at leastone characteristic value based on one or more machine parametersobserved during operation of the earth working machine, the one or moremachine parameters being selected from the group consisting of: millingdepth; advance speed; milling drum rotation speed; torque currentlyapplied to a milling drum; and power output currently being delivered bya drive engine.
 9. The method of claim 4, wherein the at least onecharacteristic value is stored in a memory of the controller, and thecontroller determines the remaining work output of the earth workingmachine based upon the second wear state and the at least onecharacteristic value.
 10. The method of claim 9, wherein the controllerand the memory are located on the earth working machine.
 11. The methodof claim 9, wherein the controller and the memory are located in aseparate control system separate from the earth working machine.
 12. Themethod of claim 11, wherein the earth working machine and the separatecontrol system are in mutual communication via a wireless remote datatransfer link.
 13. The method of claim 1, further comprising:determining a second wear state for each of a plurality of earth workingtools of the earth working machine; and determining a remaining workoutput for the earth working machine based upon each one of theplurality of earth working tools having at least a threshold residualwear capacity.
 14. The method of claim 1, further comprising: before thethird wear state of the at least one earth working tool is reached,informing a technician that tool maintenance is needed.
 15. The methodof claim 14, wherein the step of informing a technician includeswirelessly conveying a signal to the technician from the earth workingmachine or from a control system separate from the earth workingmachine.
 16. The method of claim 14, further comprising signaling theremaining work output in terms of at least one of: a distance that canstill be milled by the earth working machine; a volume that can still bemilled by the earth working machine; a mass that can still be milled bythe earth working machine; and a remaining service life of the earthworking machine.
 17. The method of claim 14, further comprising:planning a working process; and determining maintenance intervals forthe earth working machine as a function of predicted remaining workoutput for each of a plurality of earth working tools as a function ofthe planned working process.